1. Field of the Invention
The invention relates to a data processor having a function of performing radio communication, and more particularly to a data processor 10 including a signal processor such as a microprocessor, which operates in accordance with clock signals. The invention also relates to a method of controlling a frequency of clock signals in accordance with which a microprocessor operates. The invention further relates to a recording medium readable by a computer, storing a program therein for causing a computer to act as a data processor or carry out a method of controlling a frequency of clock signals in accordance with which a microprocessor operates.
2. Description of the Related Art
A data processor having a function of performing radio communication generally includes a microprocessor for data processing. However, such a data processor is accompanied with a problem that operation clocks in accordance with which a microprocessor operates act as noises to thereby degrade quality of received radio signals. In order to overcome such a problem, Japanese Unexamined Patent Publication No. 7-99680 has suggested a method of decreasing a frequency of operation clocks while a radio signal is being received.
Reduction in a frequency of operation clocks is effective for noise reduction as follows. In general, operation clocks in a microprocessor is in proportion to current consumption. Accordingly, it would be possible to reduce electric power of noises by reducing a frequency of operation clocks to thereby reduce electric power consumption. In addition, reduction in a frequency of operation clocks is further accompanied with reduction in electric power of higher-order harmonics produced by operation clocks. Since the above-mentioned method of switching a frequency of operation clocks is effective for reducing current consumption of a device, the method has been adopted in many mobile communication devices.
However, in the above-mentioned method, a frequency of operation clocks in a microprocessor is always caused to reduce, while a radio signal is being received, regardless of whether quality of a received radio signal is acceptable or not. As a result, even if quality of a received signal is acceptable and noises are sufficiently small, a frequency of operation clocks is reduced, which means that a microprocessor operate at a lower speed.
In addition, if a frequency of operation clocks is reduced, a response speed in response to a user's operation is also reduced. In accordance with the above-mentioned method, reliability in radio communication takes precedence over high-speed operation of a microprocessor while a radio signal is being received, and thus, a user is not allowed to select high-speed operation over reliability in radio communication.
Furthermore, a user cannot notice reduction in a frequency of operation clocks until he or she knows an actual response speed of a microprocessor.
Japanese Unexamined Patent Publication No. 4-122130 has suggested a mobile radio communication device including a controller, a radio transmitting and receiving section, a rechargeable internal power source to be charged through an external power source, and a switch for turning on or off an electrical path between the external power source and the internal power source. The controller closes the switch to thereby cause the external power source to charge the internal power source while the radio transmitting and receiving section is ceased to operate, and opens the switch to thereby separate the external power source from the radio transmitting and receiving section and cause the internal power source to charge the radio transmitting and receiving section while the radio transmitting and receiving section is operating.
In accordance with the above-mentioned mobile radio communication device, it is possible to suppress noises caused by operation clocks transmitted to the controller, while the radio transmitting and receiving section is caused to cease its operation. However, since the controller operates in accordance with operation clocks while the radio transmitting and receiving section is operating, a problem remains unsolved that quality of a received signal is deteriorated due to noises caused by operation clocks transmitted to the controller, while the radio transmitting and receiving section is in operation.